Parent Substrate, Wafer Composite and Methods of Manufacturing Crystalline Substrates and Semiconductor Devices

ABSTRACT

Provided is a machining apparatus including a profile sensor unit configured to obtain shape information about a parent substrate; and a laser scan unit configured to direct a laser beam onto the parent substrate, wherein a laser beam axis of the laser beam is tilted to an exposed main surface of the parent substrate, and wherein a track of the laser beam on the parent substrate is controllable as a function of the shape information obtained from the profile sensor unit.

TECHNICAL FIELD

The present disclosure is related to a method of manufacturing acrystalline substrate, in particular a crystalline device substrate, toa method of manufacturing a semiconductor device, to a crystallinesubstrate, and to a wafer composite including a crystalline substrate.

BACKGROUND

Crystalline substrates like crystalline semiconductor substrates aretypically available in standard sizes, wherein the standard definesdiameter and thickness. On the other hand, attempts have been made toreduce the final thickness of thin semiconductor devices to improvedevice characteristics. For example, for power semiconductor deviceswith a vertical load current flow between a front side and a back side,a thinner semiconductor die may result in lower on-state resistance.Other attempts aim at reducing substrate costs by using thinsemiconductor slices as base for epitaxial growth. For example,splitting methods horizontally split thin slices from semiconductorboules or horizontally split standard wafers (wafer twinning).Crystalline substrates like semiconductor wafers may be slightlychamfered, e.g., beveled and/or rounded to avoid chipping and to reducethe occurrence of fractures at sharp edges of the crystalline substrate.

There is a steady need for improving the manufacturing of crystallinesubstrates and semiconductor devices.

SUMMARY

An embodiment of the present disclosure relates to a method ofmanufacturing a device substrate. A parent substrate is provided thatincludes a central region and an edge region. The edge region surroundsthe central region. A detachment layer is formed in the central region.The detachment layer extends parallel to a main surface. The detachmentlayer includes modified substrate material. A groove is formed in theedge region. The groove laterally encloses the central region. Thegroove runs vertically and/or tilted to the detachment layer.

A further embodiment of the present disclosure relates to a parentsubstrate. The parent substrate includes a central region and an edgeregion. The edge region surrounds the central region. A groove in theedge region laterally encloses the central region. The groove runsvertically and/or tilted to the detachment layer. In the central region,a detachment layer extends parallel to the main surfaces and ends at thegroove. The detachment layer includes modified substrate material.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the embodiments and are incorporated in and constitutea part of this specification. The drawings illustrate embodiments of acrystalline substrate, a wafer composite, a method of manufacturing acrystalline substrate, and a method of manufacturing a semiconductordevice and together with the description serve to explain principles ofthe embodiments. Further embodiments are described in the followingdetailed description and the claims.

FIGS. 1A-1C illustrate schematic vertical cross-sectional views of acrystalline parent substrate for illustrating a method of manufacturinga device substrate using a groove in an edge region and a detachmentlayer in a central region according to an embodiment.

FIG. 2 is a schematic plan view of a parent substrate including a groovein an etch region according to an embodiment.

FIG. 3 is a schematic plan view of a portion of a parent substrate froma semiconductor material including a groove between a central region andan edge region according to an embodiment.

FIGS. 4A-4E are schematic vertical cross-sectional views of an edgeregion of a parent substrate with grooves of different shape accordingto embodiments.

FIGS. 5A-5G are schematic vertical cross-sectional views of a parentsubstrate based on a semiconductor material and of wafer compositesincluding the parent substrate for illustrating a method ofmanufacturing semiconductor devices according to an embodiment.

FIGS. 6A-6C are schematic vertical cross-sectional views of a parentsubstrate based on a semiconductor material and of wafer compositesincluding the parent substrate for illustrating a method ofmanufacturing semiconductor devices according to an embodiment includinglayer transfer and epitaxial growth.

FIGS. 7A-7B are schematic vertical cross-sectional views of a parentsubstrate based on a semiconductor material and of wafer compositesincluding the parent substrate for illustrating a method ofmanufacturing semiconductor devices according to an embodiment relatedto the formation of a groove on a substrate back side.

FIGS. 8A-8B are schematic vertical cross-sectional views of a portion ofa wafer composite and a trimming tool according to an embodimentreferring to an edge trim.

FIGS. 9A-9B are schematic vertical cross-sectional views of a portion ofa wafer composite according to further embodiments referring to theformation of a groove from the front side.

FIG. 10 is schematic vertical cross-sectional view of a wafer compositeaccording to an embodiment referring to front side machining.

FIGS. 11A-11D are schematic vertical cross-sectional views of a wafercomposite according to embodiments referring to back side machining.

FIG. 12 is a schematic block diagram of a tool assembly suitable forperforming front side and/or back side machining according to a furtherembodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings, which form a part hereof and in which are shownby way of illustrations specific embodiments in which a devicesubstrate, a wafer composite, a method of manufacturing a devicesubstrate, and a method of manufacturing a semiconductor device may bepracticed. It is to be understood that further embodiments may beutilized and structural or logical changes may be made without departingfrom the scope of the present disclosure. For example, featuresillustrated or described for one embodiment can be used on or inconjunction with further embodiments to yield yet a further embodiment.It is intended that the present disclosure includes such modificationsand variations. The examples are described using specific language,which should not be construed as limiting the scope of the appendingclaims. The drawings are not scaled and are for illustrative purposesonly. Corresponding elements are designated by the same reference signsin the different drawings if not stated otherwise.

The terms “having”, “containing”, “including”, “comprising” and the likeare open, and the terms indicate the presence of stated structures,elements or features but do not preclude additional elements orfeatures. The articles “a”, “an” and “the” are intended to include theplural as well as the singular, unless the context clearly indicatesotherwise.

Ranges given for a parameter include the boundary values. For example, arange for a parameter y from a to b reads as a≤y≤b. A parameter y with avalue of at least c reads as c≤y and a parameter y with a value of atmost d reads as y≤d.

Main constituents of a layer or a structure from a chemical compound oralloy are such elements which atoms form the chemical compound or alloy.For example, nickel and silicon are the main constituents of a nickelsilicide layer and copper and aluminum are the main constituents of acopper aluminum alloy.

The term “on” is not to be construed as meaning only “directly on”.Rather, if one element is positioned “on” another element (e.g., a layeris “on” another layer or “on” a substrate), a further component (e.g., afurther layer) may be positioned between the two elements (e.g., afurther layer may be positioned between a layer and a substrate if thelayer is “on” said substrate).

The term “power semiconductor device” refers to semiconductor deviceswith high voltage blocking capability, for example 30V, 100V, 600V, 3.3kV or more and with a nominal on-state current or forward current of atleast 1 A, for example 10A or more.

According to an embodiment, a method of manufacturing a device substratemay include providing a parent substrate. The parent substrate may becrystalline. That is to say, at least 90% or even at least 95% of theparent substrate may include crystalline material, e.g. polycrystallinematerial or single-crystalline material. The parent substrate mayinclude a central region and an edge region. The edge region maysurround the central region. For example, at least 60% (or at least 70%or even at least 80%) of the parent substrate may be part of the centralregion.

The parent substrate may be a crystal ingot (boule) of singlecrystalline material or a wafer-sized slice of single crystallinematerial (e.g., a wafer). The parent substrate may (except for modifiedsubstrate material within a detachment layer) exclusively include thesingle crystalline material or may include, in addition to a mainportion formed from the single crystalline material, modified substratematerial in a detachment layer and/or structures of other materials,e.g., conductive structures and/or insulating structures.

The single crystalline material may be a ceramic, e.g. α-Al₂O₃(sapphire), or a semiconductor material. The semiconductor material maybe, by way of example, any group IV element semiconductor, e.g. silicon(Si) or germanium (Ge), any group IV compound semiconductor, e.g.silicon carbide (SiC) or silicon-germanium (Site), or any group III/Vcompound semiconductor, such as gallium arsenide (GaAs) or galliumnitride (GaN).

For example, the material of the parent substrate may be 15R-SiC(silicon carbide of 15R polytype) or silicon carbide with a hexagonalpolytype, for example 2H-SiC, 4H-SiC or 6H-SiC, by way of example. Inaddition to the main constituents silicon and carbon, the parentsubstrate may include dopant atoms, for example nitrogen N, phosphorusP, beryllium Be, boron B, aluminum Al, and/or gallium Ga. Further, theparent substrate may include unwanted impurities, for example hydrogen,fluorine, and/or oxygen.

For example, the parent substrate may be a virgin semiconductor wafer ora processed semiconductor wafer. A virgin semiconductor wafer may be asemiconductor wafer at a stage after having been obtained from a crystalingot, e.g. by sawing, and prior to any conditioning specific for acertain type of semiconductor device. For example, a virginsemiconductor wafer may have been subjected to unspecific processes,e.g., edge rounding, beveling, heat treatments and/or a process thatforms a surface oxide. A processed semiconductor wafer may be asemiconductor wafer after having been subjected to at least onedevice-specific process, e.g., a blanket doping or a patterning process.A processed semiconductor wafer may include spatially separated dopedregions, insulator structures and/or conductive structures that includepolycrystalline semiconductor material, a metal, and/or a metalcompound.

The parent substrate may have two essentially parallel main surfaces ofthe same shape and size and a lateral outer surface connecting the edgesof the two main surfaces. The parent substrate may laterally extend in aplane spanned by lateral directions. Accordingly, the parent substratemay have a surface extension along two lateral directions (alsodenominated as horizontal directions in the following). The parentsubstrate may have a thickness along a vertical direction perpendicularto the lateral directions.

Here and in the following, a first and a second face may be “essentiallyparallel” if an average plane that approximates the first face enclosesan angle of at most 5 degree (or at most 2 degree) with an average planethat approximates the second face.

The main surfaces may be oriented completely planar. The main surfacesand the lateral outer surface may be connected via right-angled edges.Alternatively, the lateral outer surface may be chamfered, for examplebeveled and/or rounded in direction of one of the main surfaces or indirection of both main surfaces.

The lateral outer surface may include a vertical portion running alongthe vertical direction. In addition to the vertical portion, the lateralouter surface may include one or more beveled portions between thevertical portion and a first one of the main surfaces. In addition, thelateral outer surface may further include one or more beveled portionsbetween the vertical portion and a second one of the main surfaces. Eachbeveled portion may have another tilt angle with regard to the verticalportion. Alternatively, the lateral outer surface may include a roundedportion between the vertical portion and at least a first one of themain surfaces. The lateral outer surface may include one or more roundedportions between the vertical portion and beveled portion, betweenneighboring beveled portions and/or between a beveled portion and therespective main surface.

A first main surface at the front side and a second main surface at theback side may have the shape of a polygon (e.g. a rectangle or ahexagon) with or without rounded edges, or a circle with or without anotch or a flat along the circumference.

In a vertical cross-section, the lateral outer surface may be planar,may be outwardly bowed, and/or may include a chamfered portion at leastat one of the transitions to the main surfaces. The chamfered portionmay be beveled and/or rounded.

The main surfaces may laterally extend in a plane spanned by lateraldirections. Accordingly, the parent substrate may have a lateralextension along two orthogonal lateral directions and may have athickness along a vertical direction perpendicular to the lateraldirections.

The parent substrate may be a semiconductor wafer, wherein a diameterand a thickness of the parent substrate may correspond to a productionstandard for semiconductor wafers. The diameter of the parent substratemay be 4 inch (100 mm), 6 inch (150 mm), 7 inch (175 mm), 200 mm (8inch) or 300 mm (12 inch).

The central region of the parent substrate may be a circular or almostcircular region. In case the parent substrate is a virgin semiconductorwafer, at least the central region may be homogeneously doped. In caseof preprocessed semiconductor wafers, the central region may include aplurality of laterally separated device regions, wherein each deviceregion may include a plurality of doped regions, conductive structuresand/or insulating structures. The conductive structures and/or theinsulating structures may be formed on the parent substrate and/or mayextend from the first main surface into the parent substrate. Agrid-shaped kerf region may separate the device regions in the centralregion of the parent substrate.

The edge region may be between the central region and the lateral outersurface of the parent substrate. The edge region may extend from thecentral region to the lateral outer surface. The edge region may bewithout device regions. The edge region may completely surround thecentral region. The edge region may have an approximately uniform width.For example, the edge region may have a mean width of at least 100 μmand at most 3 mm, e.g. at most 1 mm or at most 500 μm. It may bepossible that the edge region includes or is defined by a chamfered(e.g., beveled and/or rounded) region of the parent substrate along thelateral outer surface. The chamfered region of the parent substrate maybe defined by the lateral extension of the chamfered portion of thelateral outer surface. For example, the edge region may include, e.g.may exclusively include a portion of the lateral outer surface, e.g. thechamfered portion of the lateral outer surface.

A detachment layer may be formed in the central region. The detachmentlayer may extend parallel to at least one of the main surfaces of theparent substrate or to both main surfaces. The detachment layer may bespanned by and/or may run parallel to the lateral directions.

Before or after or even during forming the detachment layer, a groovemay be formed in the edge region. It may also be possible that a part ofthe groove is formed before forming the detachment layer and a furtherpart of the groove is formed after forming the detachment layer or viceversa a part of the detachment layer is formed before forming the grooveand a further part of the detachment layer is formed after forming thegroove. The groove may consist of a single, connected groove or of aplurality of sub-grooves that are laterally separated from another. Thegroove may extend in a direction out of a layer in which the detachmentlayer is formed.

The groove may extend from one of the main surfaces up to the detachmentlayer or beyond the detachment layer. A vertical extension of the groovemay be at least 80%, e.g. at least 95% and at most 120%, e.g. 105% of adistance between the detachment layer and that main surface, in whichthe groove is formed. For example, the vertical extension of the grooveand the distance between the detachment layer and that main surface, inwhich the groove is formed, may be equal or approximately equal.

In some embodiments, the groove may extend from at least one of the mainsurfaces into the parent substrate or may extend from a portion of thelateral outer surface close to one of the main surfaces into the parentsubstrate. The groove may extend vertically and/or tilted to thedetachment layer and/or to the lateral directions. Here and in thefollowing, “tilted” may mean that the groove (e.g., a main axis of thegroove) and the detachment layer and/or the lateral directions enclosean angle of at least 5 degree and at most 90 degree. For example, thegroove and the detachment layer enclose an angle in a range from 5degree to 85 degree, e.g. in a range from 5 degree to 45 degree.

An angle of 90 degree is also fulfilled for a “vertical” groove. Themain axis of the groove may be the direction along which the groovemainly extends away from the central region. For example, the groove mayhave its largest extension away from the central region along the mainaxis. The main axis may run perpendicular or at least tilted to acircumferential direction of the parent substrate.

The groove may include an inner groove sidewall and an outer groovesidewall. The inner groove sidewall may be positioned closer to thecentral region than the outer groove sidewall. In some embodiments, thegroove may end at the detachment layer and the detachment layer may endat the groove. The detachment layer may be in contact with the innergroove sidewall. According to some embodiments, the groove may taper anda blind end of the groove and an outer edge of the detachment layer maymerge.

The detachment layer may include modified substrate material. Themodified substrate material may form a plurality of laterally separatedmodified zones. Each modified zone may be arranged along a modifiedline. In some embodiments, the detachment layer may include a pluralityof laterally separated modified zones that are arranged along modifiedlines and separated by not-modified substrate material. For example,each modified zone may include a plurality of modified regions thatarise from essentially single shots with a laser beam into the parentsubstrate. At least some or all of the modified regions may be connectedwith and/or may overlap with their neighboring modified region. Inaddition or as an alternative, it may be possible that at least some orall neighboring modified regions are separated from each other bynon-modified substrate material. That is to say, at least some of themodified regions or all of the modified regions may not overlap withneighboring modified regions. The modified lines may run parallel to oneanother. The modified zones (e.g., the modified lines) may end at theinner groove sidewall. According to another example, the modified zonesand the bottom of the groove may merge.

The modified substrate material may include the main constituents of thematerial of the parent substrate. For example, the modified substratematerial may have a phase that is different from the phase of thenon-modified material, e.g., a phase that is different from a singlecrystalline phase. For example, the modified zones may include the mainconstituents of the substrate material in polycrystalline form, inamorphous form, and/or as a mixture of the elementary constituents ofthe substrate material. For example, the modified substrate material mayinclude elementary silicon in amorphous and/or polycrystalline formand/or carbon in amorphous and/or polycrystalline form.

According to some embodiments, the detachment layer may includestructures of higher porosity, for example of a porosity of at least 20%and/or structures with implantation-induced crystal damage.Implantation-induced crystal damage may include crystal defectsdecorated with, e.g., hydrogen atoms.

The groove may laterally enclose the central region. For example, thegroove may laterally enclose the central region completely. The groovemay form a frame for the central region. The groove may have anapproximately uniform radial extension (width) along the completecircumference. The groove may have approximately uniform depth along thecomplete circumference. If the groove includes a plurality ofsub-grooves, the sub-grooves may have approximately equal width and/orequal depth along the complete circumference of the central region. In ahorizontal plane the groove may include a circular portion or mayapproximate a circular portion with orthogonal line portions.

For example, the groove may form a complete circle in the horizontalplane. The diameter of the circle may be smaller than the largestinscribed circle of the horizontal substrate shape, which may includeone or more flats along the outer circumference. The groove may bevertical or may be tilted in direction to the center of the circle,wherein an angle between a main axis of the groove and the horizontalplane may be in a range from 5 degree to 45 degree, e.g. from 15 degreeto 45 degree. The groove may be exclusively formed in a portion of theedge region in which the main surfaces are parallel to each other.Alternatively, the groove may be partly or completely formed in achamfered and/or rounded portion of the edge region. For example, thegroove may be formed completely or in parts in the lateral outersurface.

According to another example, the groove may include one or morestraight portions and one or more circular arcs, wherein the one or morestraight portions and the one or more circular arcs complement eachother to a closed form. The diameter of the circular arcs may besmaller, equal to or greater than the largest inscribed circle of thehorizontal substrate shape, which may include one or more flats alongthe outer circumference. Each straight portion of the groove may runparallel to one flat. The groove may be vertical or may be tilted indirection to the center of the circle, wherein an angle between a mainaxis of the groove and the horizontal plane may be in a range from 5degree to 45 degree, e.g. from 15 degree to 45 degree. The groove may beexclusively formed in a portion of the edge region in which the mainsurfaces are parallel to each other. Alternatively, the groove may bepartly or completely formed in a chamfered and/or rounded portion of theedge region. For example, the groove may be formed completely or inparts in the lateral outer surface.

The groove may include an inner groove sidewall at a side orientedtowards the central region (e.g., a lateral center) of the parentsubstrate. The groove may be formed at a distance to the central region.A distance between the groove and the central region may be uniformalong the complete circumference. According to another example, theinner groove sidewall may mark the boundary or the transition betweenthe central region and the edge region. A width of the groove may be atleast 10 μm. A depth of the groove (e.g., an extension of the groovealong the main axis) may be in a range from 10 μm to several hundred μm.

The combination of a circumferential groove and a detachment layer incontact with an inner groove sidewall may facilitate a later splittingof the parent substrate into a device substrate and a reclaim substrate,wherein the device substrate and the reclaim substrate separate along asplitting surface extending laterally through and/or along and/oressentially parallel to the detachment layer. The groove may avoid or atleast attenuate edge effects that may adversely affect the formation ofa portion of the detachment layer close to the lateral outer surface.

According to an embodiment, the parent substrate may be split along asplitting surface through, e.g. in the detachment layer. The splittingsurface may vertically divide the detachment layer into a portion abovethe splitting surface (e.g., a first parent substrate portion) and intoa portion below the splitting surface (e.g., a second parent substrateportion). The splitting divides the parent substrate into a first parentsubstrate portion (device substrate) and a second parent substrateportion (reclaim substrate). The first parent substrate portion mayinclude the parent substrate portion extending from the first mainsurface to the splitting surface. The second parent substrate portionmay include the parent substrate portion extending from the splittingsurface to the second main surface.

Owing to the groove, the splitting process may be independent from edgeeffects; such edge effects may adversely affect the yield of thesplitting process. In addition, it is possible to define a shape of alateral outer surface of the device substrate or a shape of a lateralouter surface of the reclaim substrate via the shape of the groove. Itis also possible to form that substrate portion, which lateral outersurface is not defined by the groove, with a ring-shaped stiffeningportion. The stiffening portion may have a greater vertical extensionthan a central portion of the concerned substrate portion.

That is to say, a device substrate obtained from the splitting processmay have intrinsically chamfered edges along the lateral outer surfaceand/or may be formed with a stiffening ring. Formation of the chamferededges and/or the stiffening ring requires no additional processes but isalready achieved by the splitting process alone. The chamfered edges mayreduce the occurrence of chipping and the occurrence of fractures alongthe lateral outer surface even for device substrates with a thicknessthat is not accessible for standard chamfering tools. The stiffeningring may mechanically stabilize the device substrate after the splittingprocess.

In addition or as an alternative, a reclaim substrate obtained from thesplitting process may have intrinsically chamfered edges and/or mayinclude a stiffening ring that stabilizes the reclaim substrate afterthe splitting process. The lateral dimension of the reclaim substrate,e.g. the diameter, may be the same as that of the parent substrate suchthat rework and/or reuse of the reclaim substrate may use standard toolswithout changes or with only uncritical changes of the set-up of suchstandard tools.

For example, when the groove may be formed completely or in parts in thelateral outer surface and extends tilted to the horizontal plane at anangle between 45 degree and 5 degree, the diameters of both the reclaimsubstrate and the device substrate may be approximately the same. Boththe device substrate and the reclaim substrate may be handled with thesame tools and the reclaim substrate may be further processed in almostthe same way as the device substrate or the parent substrate.

According to an embodiment, in the edge region a distance between themain surfaces of the parent substrate may decrease with increasingdistance to a lateral center of the parent substrate and/or withincreasing distance to the central region. In other words, the parentsubstrate may be a semiconductor wafer with the lateral outer surfacechamfered at the transition to at least one of the main surfaces. Thechamfer may include a bevel that may be rounded or not rounded. Thechamfer may contribute to reducing the occurrence of cracks and/or edgechipping effects during transport or handling of the parent substrate.According to other examples the distance between the main surfaces ofthe parent substrate may be constant within the edge region.

The circumferential groove may decouple formation of the detachmentlayer from effects of the chamfer on the formation process for thedetachment layer. For example, due to the nature of a laser-induceddamage layer formation (optical constraints and micro crack length) itmay be difficult to form a detachment layer containing laser-inducedcrystal damage in a way that the laser-induced crystal damage reachesthe lateral outer surface to a sufficient degree. In case the detachmentlayer does not reach the lateral outer surface to a sufficient degree,the crack entry from the lateral outer surface during the splittingprocess may be difficult and the yield may thus be critical. With thedetachment layer ending at the circumferential groove, it is possible toeliminate the need for a detachment layer ending at the lateral outersurface.

Other than an edge trim process that may remove semiconductor materialstarting from the lateral outer surface, the circumferential grooveextending from the direction of one of the main surfaces into the parentsubstrate may be formed at an early stage of processing. In particular,standard tools for wafer processing at the front side may be used toform the groove, for example, dicing tools, which separate the deviceregions from each other, or edge trim tools. Formation of the groove canbe easily integrated into existing manufacturing lines at low or mediumeffort.

Other than a horizontal layer etch process that may remove adhesivematerial adhering the parent substrate to an auxiliary carrier, thecircumferential groove extending from one of the main surfaces into theparent substrate may be formed without removing adhesive material andwithout that residues of the adhesive material may contaminate theparent substrate and/or the tool used for forming the groove.

According to an embodiment, the groove may extend from a first mainsurface at a front side of the parent substrate into the parentsubstrate. The front side may be that side of the pattern substrate atwhich a front side metallization of a semiconductor device, for examplethe source electrodes and gate electrodes of a power semiconductordevice are formed. In this case the groove may be formed at low ormedium additional effort with any tool adapted for a pre-dicing processin the framework of a DBG (dice before grind) process, by way ofexample. The yield of the splitting process may be significantlyimproved at only low or medium additional effort. According to otherexamples, the groove may extend from a second main surface opposite tothe front side of the parent substrate into the parent substrate.

According to an embodiment, the groove may include an inner groovesidewall. The inner groove sidewall is oriented to the lateral centerand/or the central region of the parent substrate. The inner groovesidewall may include a vertical or approximately vertical sidewallsection. In this context, the terms “vertical” and “tilted” may refer tothe orientation of the sidewall section with respect to the lateraldirections. The detachment layer may cut the vertical sidewall section.In other words, the detachment layer, e.g. the modified zones of adetachment layer including laser-induced crystal damage may end at thevertical sidewall section.

With the detachment layer cutting the inner groove sidewall orthogonallyor almost orthogonally, propagation of cracks originating from the innergroove sidewall into the direction of the lateral center of the parentsubstrate may be supported. It is possible to perform the splittingprocess with high reliability and at high yield.

According to an embodiment, the groove may be spaced from a lateralouter surface of the parent substrate. In other words, the groove may beformed at a distance to the lateral outer surface. For example, thegroove may be formed at low additional costs using a dicing blade and/ora laser ablation tool (e.g., a laser dicing tool). An opening of thegroove in the first or second main surface may have a width in radialdirection. The width of the groove opening may be in a range from atleast 10 μm (or at least 30 μm) to at most 1 mm, typically at most 300μm or at most 100 μm. For example, the groove opening may have a widthin a range from 30 μm to 60 μm. A vertical extension of the groove maybe chosen such that the groove reaches the detachment layer. Forexample, the vertical extension of the groove may be in a range from 10μm to 200 μm, for example in a range from 20 μm to 120 μm (e.g., 60 μmto 120 μm or 30 μm to 60 μm).

According to an embodiment, the groove may extend inwardly from thelateral outer surface. In other words, the groove forms a one-sidedindentation with the inner groove sidewall forming the only groovesidewall extending from the main surface into the parent substrate.Starting from the inner groove sidewall, the groove may have anapproximately flat groove bottom extending from the inner groovesidewall to the lateral outer surface. A transition between the innergroove sidewall and the groove bottom may be curved. A radial extensionof the groove corresponds to the distance of the inner groove sidewallto the outer circumference of the parent substrate. The radial grooveextension may be at least 90% and at most 110% of a width of the edgeregion. For example, the radial extension of the groove may be at least10 μm (or at least 30 μm) to at most 1 mm, typically at most 300 μm orat most 100 μm. The vertical extension of the groove may be in a rangefrom 10 μm to 200 μm, typically in a range from 20 μm to 120 μm (e.g.,60 μm to 120 μm or 30 μm to 60 μm).

The groove bottom may be parallel to the main surfaces or may be tiltedto the main surfaces such that the remaining portion of the parentsubstrate in the edge region is chamfered, for example beveled with orwithout rounding.

Forming the groove may include a spiral cut or a sequence of round-cutswith different diameters with a conventional dicing tool, for example, adicing blade for round cut, wherein the material between the innergroove sidewall and the lateral outer surface may be completely removed.

According to another example, an edge bevel tool may remove the material(e.g., completely or at least 90% of the material) between the innergroove sidewall and the lateral outer surface. The edge bevel tool maybe a grinding tool, wherein the shape of an indentation of a grindingpad may be complementary to the vertical cross-sectional shape of thegroove. The indentation may be formed such that the device substrate isformed with a chamfer along the outer lateral surface and/or such thatthe reclaim substrate is formed with a chamfer along the outer lateralsurface.

According to an embodiment, forming the groove may include alaser-assisted material removal. The laser-assisted material removal mayinclude directing a laser beam into the direction of and/or onto thefirst main surface. In an additional or alternative embodiment, thelaser-assisted material removal may include directing a laser beam intothe direction and/or onto the second main surface. In the latter case,the parent substrate may be attached with the front side down to anauxiliary carrier.

In a further additional or alternative embodiment, the laser-assistedmaterial removal may include directing a laser beam into the directionand/or onto the first main surface. In the latter case, the parentsubstrate may be attached with the side opposite to the front side downto an auxiliary carrier.

In general, the laser-assisted material removal may include weakeningand/or removing material of the parent substrate with the laser beam.The laser-assisted material removal may include or may be at least oneof: laser-assisted ablation (e.g., laser dicing) or a laser-assistedetch process. Laser-assisted ablation usually makes use of materialremoval by melting and/or evaporating and/or sublimating material with alaser beam. The laser-assisted etch process may include weakening and/orconverting the material of the parent substrate in a region where thegroove is to be formed. The weakened material may, for example, then beremoved via etching.

In general, the laser beam may be directed into the direction of alateral center of the parent substrate. For example, the laser beam maybe tilted with respect to the horizontal directions or to both thevertical direction and the horizontal directions. An angle between thevertical direction and a propagation axis of the laser beam may be atleast 30 degree. In other embodiments, the angle between the verticaldirection and the propagation axis of the laser beam may be at most 10degree, e.g. at most 5 degree or 0 degree. The laser beam may be a UVlaser beam with a peak wavelength between at least 200 nm and at most450 nm. In other embodiments, the laser beam may a visible or aninfrared laser beam, e.g. with a wavelength of at least 1 μm and at most1.8 μm. Larger wavelengths may also be possible.

The laser-assisted material removal may be controlled such that a groovewith a bowed inner groove sidewall is formed. The inner groove sidewallmay be bowed inwardly with respect to the groove. The ablation volume ofthe laser-assisted material removal may be small compared to theablation volume of a process forming the groove by means of a mechanicaldicing tool.

In some embodiments, the splitting process may form the device substratewith an intrinsically outwardly bowed lateral outer surface that may beab initio less susceptible to edge chipping. The splitting process mayform a reclaim substrate with a stiffing ring which sidewalls can befavorably shallow and/or bowed. In other words, it is possible that thestiffing ring does not include steep sidewalls and/or rectangular outeredges such that the stiffing ring may be ab initio less susceptible toedge chipping. The stiffing ring may facilitate the rework and/or reuseof thin reclaim substrates at high yield.

In some embodiments, the splitting process may form a reclaim substratewith an intrinsically outwardly bowed lateral outer surface that is abinitio less susceptible to edge chipping. The device substrate may beformed with a stiffing ring which sidewalls can be favorably shallowand/or bowed. In other words, the stiffing ring does not include steepsidewalls and/or rectangular outer edges such that the stiffing ring canbe ab initio less susceptible to edge chipping. The stiffing ring mayfacilitate the further processing of very thin device substratesobtained from the device substrates at high yield.

Demounting and handling stability for both the device substrate and thereclaim substrate can be significantly improved. Forming the groove fromthe second main surface may get along without removing any adhesivematerial or with removing only little adhesive material used fortemporarily mechanically connecting the parent substrate with anauxiliary carrier.

According to an embodiment, the method includes connecting an auxiliarycarrier and the parent substrate. The first main surface of the parentsubstrate is oriented to a working surface of the auxiliary carrier. Inother words, the first main surface of the parent substrate faces theworking surface of the auxiliary carrier. The auxiliary carrier and theparent substrate may be mechanically connected after forming the groovein the first main surface and/or prior to forming the groove in thesecond main surface. Forming the groove and splitting the parentsubstrate may leave the auxiliary carrier completely unaffected. Theauxiliary carrier may be reworked and reused at low or medium effort.

The auxiliary layer and the parent substrate may be direct bonded or abonding layer with high thermal stability may bond the first mainsurface of the parent substrate and the working surface of the auxiliarycarrier.

According to an embodiment, connecting the auxiliary carrier and theparent substrate may include forming an adhesive structure between theworking surface of the auxiliary carrier and the central region of theparent substrate. For example, adhesive material may be deposited on atleast one of the working surface of the auxiliary carrier or the firstmain surface of the parent substrate. The adhesive material may bedeposited in the central region of the parent substrate and/or in acentral portion of the working surface, wherein the central portion ofthe working surface corresponds in size and form to the central regionof the parent substrate. It is possible that the adhesive material isnot applied in the edge region. For example, the adhesive material maybe deposited in a patterned deposition process, or the adhesive materialmay be only temporarily deposited in the edge region of the parentsubstrate and later removed from the edge region.

In particular, the groove may be completely or predominantlyadhesive-free for the splitting process. The splitting process mayremain unaffected from the adhesive and it is possible that no residualsof the adhesive material are set free by the splitting process.

According to an embodiment, connecting the auxiliary carrier and theparent substrate may include forming an adhesive layer between theworking surface of the auxiliary carrier and the first main surface ofthe parent substrate. For example, the adhesive layer may be formedacross the entire first main surface. Prior to splitting, an edgeportion of the adhesive layer may be released and/or removed selectivelywith respect to a central portion of the adhesive layer in the centralregion. An auxiliary radiation beam effective only in the edge regionmay locally generate heat below a peripheral adhesive portion extendingoutwardly from the outer groove sidewall and may release the peripheraladhesive portion. According to another example, the adhesion may bereleased in the edge region, e.g. in the entire edge region and/orincluding the groove. After removal and/or release of the peripheraladhesive portion, it is possible that the adhesive material does notblock the crack entry into the detachment layer for the splittingprocess.

According to an embodiment, a method of manufacturing a semiconductordevice may include providing a device substrate, e.g. a crystallinedevice substrate, from a parent substrate according to a method asdescribed above. The parent substrate may include a semiconductormaterial. The parent substrate may be a chamfered semiconductor wafer. Asemiconductor device may be formed from a part of the device substrate.Thin semiconductor devices may be formed at low loss of expensivesemiconductor material.

According to an embodiment, a parent substrate may include a centralregion and an edge region. The edge region may surround the centralregion. The parent substrate may be any of the parent substrates asdescribed above. The parent substrate may include or may consist ofcrystalline semiconductor material, by way of example.

In the central region of the parent substrate a detachment layer mayextend parallel to a main surface. The detachment layer may includemodified substrate material. The detachment layer may be any of thedetachment layers described above.

In the edge region of the parent substrate, a groove may laterallysurround and/or enclose the central region. The groove, e.g. a main axisof the groove, may run vertically and/or tilted to the detachment layer.The groove may be any of the grooves as described above or below. Forexample, the groove may have been formed with a method as describedabove or below. The detachment layer may end at the groove. For example,the detachment layer may end at an inner groove sidewall of the groove.

According to an embodiment, a distance between the main surfaces of theparent substrate may decrease with increasing distance to a lateralcenter of the parent substrate.

According to an embodiment, the groove may include an inner groovesidewall. The inner groove sidewall may include a vertical sidewallsection. The detachment layer may cut the vertical sidewall section. Thegroove may be spaced from an outer edge of the parent substrate.Alternatively, the groove may extend inwardly from the lateral outersurface of the parent substrate.

According to an embodiment, the inner groove sidewall may be inwardlybowed with respect to the groove. Accordingly, a first substrate portionbetween the detachment layer and the first main surface may be outwardlybowed. The groove may extend from the first or from the second mainsurface of the parent substrate into the parent substrate.

For example, the groove may form a complete circle in the horizontalplane. The diameter of the circle may be smaller than the largestinscribed circle of the horizontal shape of the parent substrate,wherein the parent substrate may have one or more flats along the outercircumference. The groove may be vertical or may be tilted in directionto the center of the circle, wherein an angle between a main axis of thegroove and the horizontal plane may be in a range from 15 degree to 45degree. The groove may be exclusively formed in a portion of the parentsubstrate with the main surfaces running parallel to each other.Alternatively, the groove may be partly or completely formed in aportion where the distance between front side and the opposite sidedecreases, e.g., where the parent substrate shows a chamfer and/or arounding. For example, the groove may be formed completely or partly inthe chamfered and/or rounded part along the edge of the parentsubstrate.

According to another example, the groove may include one or morestraight portions and one or more circular arcs, wherein the one or morestraight portions and the one or more circular arcs complement eachother to a closed form. The diameter of the circular arcs may besmaller, equal to or greater than the largest inscribed circle of thehorizontal shape of the parent substrate, which may include one or moreflats along the outer circumference. Each straight portion of the groovemay run parallel to one flat. The groove may be vertical or may betilted in direction to the center of the circle, wherein an anglebetween a main axis of the groove and the horizontal plane may be in arange from 15 degree to 45 degree. The groove may be exclusively formedin a portion of the edge region in which the main surfaces are parallelto each other. Alternatively, the groove may be partly or completelyformed in a chamfered and/or rounded region of the parent substrate. Forexample, the groove may be formed completely or in parts in the lateralouter surface.

According to an embodiment, a wafer composite may include the parentsubstrate as described above and an auxiliary carrier. The auxiliarycarrier may be attached to the parent substrate, wherein the first mainsurface of the parent substrate is oriented to a working surface of theauxiliary carrier. In other words, the first main surface faces theworking surface.

According to an embodiment, the wafer composite may include an adhesivestructure between the auxiliary carrier and the central region of theparent substrate. The adhesive structure may be absent between theauxiliary carrier and the edge region of the parent substrate.

According to a further embodiment, a machining apparatus may include aprofile sensor unit and a laser scan unit. The profile sensor unit mayobtain shape information about a parent substrate. For example, theprofile sensor unit may obtain information about a horizontal shape ofthe parent substrate. In particular, the profile sensor unit may obtaininformation about the position and/or dimension of a notch or flat alongthe circumference of a parent substrate, which—apart from the notch orflat—may have a circular horizontal shape in the rest.

The laser scan unit may direct a laser beam onto the parent substrate. Alaser beam axis of the laser beam may be tilted to an exposed mainsurface of the parent substrate. An angle between the exposed mainsurface and the laser beam axis may be at least 10 degree and at most 90degree. The tilt angle is oriented such that the laser beam is directedin direction of a lateral center of the parent substrate.

The impinging site of the laser beam may be close to the outer edge ofthe parent substrate. For example, the laser beam may impinge in an edgearea of the exposed main surface, wherein the edge area is a ring-shapedstripe including the outermost 3 mm of the exposed main surface.Alternatively, the laser beam may impinge on a lateral outer surface ofthe parent substrate. Alternatively, an impinging site of the laser beammay overlap with both the edge area and the lateral surface area.

A track of the laser beam on the parent substrate is controllable as afunction of the shape information obtained from the profile sensor unit.In particular, the laser beam may follow a notch or a flat detected bythe profile sensor unit.

According to an embodiment, the machining apparatus may include a stageunit adapted to be reversibly connected with a main surface of theparent substrate. The stage unit may be moveable with respect to thelaser beam and/or the laser beam may be moveable with respect to thestage unit such that the laser beam may follow a track along thecircumference of the parent substrate. The relative movement betweenlaser beam and stage unit may include a rotational movement, a radialmovement, and/or two orthogonal linear movements. The machiningapparatus facilitates formation of grooves of any type as describedabove.

Embodiments of the method described herein may be used for manufacturingembodiments of the crystalline substrate as described herein. In atleast some embodiments of the method and/or the crystalline substrate,the following features (if applicable) apply, alone or in combination:

-   -   (i) The detachment layer ends at the groove and/or is in direct        contact with the groove.    -   (ii) Forming the groove includes a laser-assisted material        removal, for example a laser-assisted etch process and/or laser        ablation (e.g., laser dicing).    -   (iii) The laser-assisted material removal includes directing a        laser beam into a first or a second main surface of the parent        substrate.    -   (iv) The laser-assisted material removal includes directing a        laser beam completely or partly into a lateral outer surface of        the parent substrate, wherein an angle between a propagation        direction of the laser beam and a horizontal plane is at least        20 degree, e.g., at least 30 degree.    -   (v) The laser-assisted material removal includes directing a        laser beam completely or partly into a lateral outer surface of        the parent substrate, wherein an angle between a propagation        direction of the laser beam and a horizontal plane is at most 75        degree, e.g., at most 60 degree.    -   (vi) The laser beam runs essentially parallel to the vertical        direction.    -   (vii) The edge region is defined by and/or corresponds to a        beveled outer region of the parent substrate.    -   (viii) A transition between the groove bottom and the inner        groove sidewall may be rounded.

FIGS. 1A-1C illustrate an embodiment with a groove 190 formed at thefront side of a crystalline parent substrate 100.

The parent substrate 100 of FIG. 1A may include a ceramic, e.g. sapphireα-Al₂O₃, or a semiconductor, for example silicon carbide of a hexagonalpolytype. The parent substrate 100 may be a virgin substrate after cutfrom a crystal boule or may be a processed substrate, e.g., asemiconductor wafer. A first main surface 101 at a front side and asecond main surface 102 at a back side extend mainly parallel to eachother. The second main surface 102 may have the same shape and size asthe first main surface 101. The first and second main surfaces 101, 102may be approximately planar or may be ribbed. The first main surface 101and/or the second main surface 102 may be tilted to a plane of ahexagonal crystal lattice of the parent substrate 100 by an off-axistilt of about 4 degree. A lateral outer surface 103 connects the edge ofthe first main surface 101 and the edge of the second main surface 102.

The parent substrate 100 may include a central region 110 and an edgeregion 180 between the central region 110 and the outermost edge of thelateral outer surface 103. The central region 110 may include aplurality of device regions 115. The edge region 180 is free of deviceregions 115.

The device regions 115 are arranged in lines and rows. A grid-shapedkerf region 116 laterally separates the device regions 115 from eachother. Each device region 115 may include at least some of thestructures defining an integrated circuit. The integrated circuit may bea power semiconductor device. Each device region 115 may includestructures formed on a semiconducting main portion of the parentsubstrate. For example, a front side metallization may be formed on thesemiconducting main portion. The front side metallization may include afirst load electrode of a power semiconductor device and, if applicable,a control electrode, for example a gate electrode of an MOSFET (metaloxide semiconductor field effect transistor), an IGBT (insulated gatebipolar transistor), or a JFET (junction field effect transistor).

The groove 190 is formed in the edge region 180. A detachment layer 150is formed in the central region 110. The detachment layer 150 may beformed prior to or after the groove 190. For example, the detachmentlayer 150 may be formed prior to the groove 190 to avoid edge effectsthat may affect the formation of the detachment layer 150 in a regionclose to the groove 190. According to another example, the groove 190may be formed prior to the detachment layer 150, wherein the formationof the groove 190 may be combined with front side processing and theformation of the detachment layer may be combined with a back sideprocess, e.g. a laser treatment from the back side.

The detachment layer 150 shown in FIG. 1B may include modifiedstructures that include material of the parent substrate in modifiedform. The modified structures may include porous material,implantation-induced crystal damage, and/or laser-induced materialmodifications. The modified stripes are laterally separated by stripesof non-modified material. In addition, the detachment layer may includemicrocracks extending along main crystal planes, for example along thea-planes. The microcracks may originate at the modified stripes and/ormay pass the modified stripes in close vicinity.

A first distance d1 between the detachment layer 150 and the first mainsurface 101 may be smaller than a first vertical extension v1 of thegroove 190. The groove 190 may be formed with a tool suitable for frontside processing in the field of manufacturing semiconductor devices. Forexample, the groove 190 may be formed using an edge trim wheel, a dicingblade, and/or a patterned etch process, for example reactive ion beametching. Alternatively, the groove may be formed with a dedicated tooldesigned for forming the groove 190, e.g. by plasma etching using avertical or tilted laser beam. The groove 190, e.g. a main axis 194 ofthe groove 190, runs parallel to a vertical direction 104.

Prior to or after forming the groove 190, a grid-shaped dicing grid (notillustrated) may be formed in the kerf region 116. The dicing grid mayextend from the first main surface 101 into the parent substrate 100. Avertical extension of the dicing grid may be smaller than the firstdistance d1 between the first main surface 101 and the detachment layer150.

In the illustrated example the groove 190 extends from the first mainsurface 101 at the front side into the parent substrate 100. Accordingto another example (not illustrated) the groove 190 extends from thesecond main surface 102 on the back side into the parent substrate 100.

In the illustrated example the groove 190 extends vertically into theparent substrate 100. According to another example (not illustrated) thegroove 190 is tilted against the vertical direction at an angle in arange from 5 degree to 85 degree in direction of the lateral center ofthe parent substrate 100, wherein the groove 190 may extend from thefirst main surface 101 or from the second main surface 102 into theparent substrate 100.

In the illustrated example the groove 190 extends from a horizontalsurface section into the parent substrate 100. According to anotherexample (not illustrated) the groove 190 extends partly or completelyfrom a non-horizontal surface section of the first main surface or froma non-horizontal surface section of the second main surface 102 into theparent substrate 100, wherein the groove 190 may be vertical or tiltedagainst the vertical direction at an angle in a range from 5 degree to85 degree in direction of the lateral center of the parent substrate100. The non-horizontal surface section may be a chamfered and/orrounded surface portion.

A splitting process may split the crystalline parent substrate 100 alonga ribbed splitting surface 155. The splitting surface 155 forms withinthe detachment layer 150. In case the detachment layer 150 is based onlaser-induced modifications of the material of the parent substrate 100,the splitting process may include the application of volumetric latticestress. The volumetric lattice stress may be applied through ultrasonicwaves or by generating thermomechanical stress. For example, a polymerfoil may be attached to the first main surface 101 or to the second mainsurface 102. The parent substrate 100 and the polymer foil may be cooledto below the glass transition temperature of the polymer foil. Thepolymer foil contracts and induces volumetric lattice stress in theparent substrate 100. The mechanical stress induces the propagation ofmacro-scale cracks propagating along main lattice planes, e.g. thea-planes, wherein yet existent micro-cracks merge to a ribbed splittingsurface 155 that extends mainly laterally through the detachment layer150. Generation of the splitting surface 155 starts at the exposed edgeof the detachment layer 150 in the groove 190. A steep sidewall of agroove 190, which is not filled with a solid material but which may befilled with a fluid, may facilitate a highly reproducible course of thesplitting process.

As shown in FIG. 1C, the parent substrate of FIG. 1B splits into a firstparent substrate portion and a second parent substrate portion. Thefirst parent substrate portion (device substrate 410) includes a portionof the parent substrate 100 between the first main surface 101 of FIG.1B and the splitting surface 155. The second parent substrate portion(reclaim substrate 420) includes the portion of the parent substrate 100between the splitting surface 155 and the second main surface 102 ofFIG. 1B.

The device substrate 410 includes a first detachment layer portion 416and a first substrate portion 415 with a lateral outer surface 413. Thereclaim substrate 420 includes a second substrate portion 425 and asecond detachment layer portion 426. The reclaim substrate 420 includesa stiffing ring 427 that protrudes above the second detachment layerportion 426 along an outer circumference of the reclaim substrate 420.

FIG. 2 shows a schematic plan view of a cylindrical parent substrate100. As a mere example, a lateral outer surface 103 of the parentsubstrate 100 includes a flat portion 106. In other embodiments, thelateral outer surface 103 may include a notch portion or may includemore than one flat portion. A groove 190 may completely surround acentral region 110. The groove 190 may include a circular portion 199and a linear portion 198. The circular portion 199 may form or mayapproximate a segment of a circle, wherein a center of the circlecoincides with a lateral center 105 of the parent substrate 100. Thelinear portion 198 may extend parallel to the flat portion 106 of thelateral outer surface 103. The circular portion 199 and the line portion198 may complement each other to a contiguous frame withoutinterruptions.

The circular portion 199 may form a segment of a circle and may beformed by a point-symmetric process, e.g., a round cut or an edge trim.Alternatively, the circular portion 199 may include orthogonal linearsections such that the groove 190 follows a stepped line thatapproximates a segment of a circle and wherein the circular portion 199may be formed by a process tool using Cartesian coordinates, e.g. forgenerating an etch mask on the first main surface 101.

According to another example (not illustrated) the groove 190 may be acircle.

FIG. 3 shows a central region 110 including device regions 115 and agrid-shaped dicing grid 117 laterally separating the device regions 115from each other. A groove 190 separating the device regions 115 from anedge region 180 may include orthogonal linear portions in the lateralprojection of the line sections of the dicing grid 117. The groove 190may have a greater vertical extension than the dicing grid. The groove190 may have a greater lateral width than the line sections of thedicing grid 117 and/or may have another vertical cross-sectional shapeas the lines sections of the dicing grid 117. According to anembodiment, the groove 190 may be laterally separated from the dicinggrid 117.

FIGS. 4A-4E show vertical cross-sections of grooves 190 extending from afirst main surface 101 into a parent substrate 100 as well as possiblepositions of the detachment layer 150 in relation to the groove 190. Theparent substrate 100 includes a chamfer 185 between the outer edge ofthe first main surface 101 and a straight vertical portion at theoutermost edge of the lateral outer surface 103. The chamfer 185 formspart of the lateral outer surface 103. Main axes 194 of the grooves 190run vertically or tilted to a vertical direction 104.

In FIG. 4A the groove 190 extends inwardly from the lateral outersurface 103. The groove 190 has only an inner groove sidewall 191oriented to the lateral center of the first main surface 101. A radialextension (width) of the groove 190 is equal to the distance of theinner groove sidewall to the outer circumference of the parentsubstrate. The radial groove extension may be at least 90% and at most110% of a width of the edge region.

A groove bottom 195 may extend approximately in a plane parallel to thefirst main surface 101. According to other examples, the groove bottom195 may slightly fall or may slightly rise with decreasing distance tothe lateral outer surface 103.

A transition between the groove bottom 195 and the inner groove sidewall191 may be rounded, wherein a radius r1 of the rounding may be in arange from 0.5 μm to 50 μm, typically in a range from 1 μm to 15 μm orin a range from 20 μm to 30 μm. This rounded transition between thegroove bottom and the inner groove sidewall may arise from the tool(e.g., a dicing tool, a trimming tool and/or a grinding tool) used forpreparing the groove. Owing to mechanical abrasion of the tool, thegroove may not be cut precisely but rather is rounded. The radius causedby tool may be taken into account when preparing the groove, for examplewhen defining the width and/or the vertical extension of the groove.Between the first main surface 101 and the rounding, the inner groovesidewall 191 may include a vertical or approximately vertical sidewallsection 193. The detachment layer 150 may cut the inner groove sidewall191 in the vertical sidewall section 193.

FIGS. 4B and 4C refer to grooves 190 with symmetrically formed inner andouter groove sidewalls 191, 192. The width of the grooves 190 in radialdirection with respect to a lateral center of the parent substrate maydecrease with increasing distance to the first main surface 101 in stepsas illustrated in FIG. 4B or continuously as illustrated in FIG. 4C. Theopenings of the grooves 190 in the first main surface 101 have a widthin radial direction.

A portion of the inner groove sidewall 191 between the first mainsurface 101 and the detachment layer 150 defines the lateral outersurface 413 of a device substrate 410 that may be obtained from theparent substrate 100 by splitting along a splitting surface through thedetachment layer 150. The stepped or tilted groove sidewalls 191 yieldadvanced etch profiles for the device substrate 410. Edge chipping andthe risk of breakage during dismount can be reduced at least for processsteps that handle the device substrate 410 directly after the splittingprocess. The tilted and/or stepped inner groove sidewalls 191 mayfacilitate edge beveling of thin and ultrathin substrate portions. Athin or ultrathin substrate portion may have a diameter in the range ofusual wafer diameters and a thickness of at most 120 μm, for example atmost 80 μm or even at most 60 μm. The outer groove sidewall 192 maydefine the shape of the inner sidewall of the stiffing ring 427 of thereclaim substrate 420.

FIGS. 4D-4E refer to asymmetric inner and outer groove sidewalls 191,192. For example, the inner groove sidewall 191 may include a steepersection as the outer groove sidewall 192. In the steep or almostvertical sidewall section 193 the detachment layer 150 may cut the innergroove sidewall 191 orthogonally or almost orthogonally for a reliablesplitting process induced by volumetric lattice stress. Above and/orbelow the vertical sidewall section 193, the inner groove sidewall 191may be slightly rounded or beveled. The outer groove sidewall 192 may besignificantly shallower than the inner groove sidewall 191. The chamfer185 and the inner groove sidewall 192 define the sidewalls of a stiffingring 427. A stiffing ring 427 with shallow sidewalls may be robustagainst chipping and may facilitate a less complicate handling of thereclaim substrate 420.

In FIG. 4E the groove 190 may be formed by plasma etching that may use atilted laser beam. The groove 190 may taper with increasing distance tothe first main surface 101. The inner groove sidewall 191 may be bowed.The bow may extend inwardly with respect to the groove 190 and outwardlywith respect to the device substrate 410. In addition, the outersidewall 192 may be outwardly bowed with respect to the groove 190 andinwardly bowed with respect to the stiffing ring 427. The detachmentlayer 150 may end at or in close vicinity to the blind end of thetapering groove 190.

According to other examples (not illustrated), the grooves 190 asdescribed with reference to FIGS. 4A-4E extend from the second mainsurface 102 into the parent substrate 100.

FIGS. 5A-5G illustrate a method of manufacturing a semiconductor device,for example a vertical silicon carbide power semiconductor device.

FIG. 5A shows a parent substrate 100, which may be a processed chamferedsilicon carbide wafer with a standard diameter and with a standardthickness. The parent substrate 100 includes a central region 110 and anedge region 180 surrounding the central region 100. The edge region 180separates the central region 110 from a lateral outer surface 103. Inthe edge region 180 the parent substrate 100 includes a chamfer 185. Thechamfered portion may include bevel planes and/or roundings, e.g.,roundings between neighboring bevel planes and between bevel planes andthe main surfaces 101, 102.

The central region 110 includes a plurality of device regions 115. Theedge region 180 is free of device regions 115. The device regions 115are arranged in lines and rows and a grid-shaped kerf region 116laterally separates the device regions 115 from each other. In eachdevice region 115, several doped regions may be formed. For example, theparent substrate 100 may have a background doping of a firstconductivity type and each device region 115 may include one or moreemitter regions 120 of a complementary second conductivity type. Theemitter regions 120 may be in contact with the first main surface 101.The emitter regions 120 may be the anode regions of power semiconductordiodes or may include body regions of power switching devices includingtransistor cells. A front side metallization 171 may be formed on thefirst main surface 101. The front side metallization 171 may be incontact with the emitter regions 120. Portions of an interlayerdielectric 160 may be formed between portions of the front sidemetallization 171 and the first main surface 101. Passivation structures(not illustrated) may cover edges of the front side metallization 171. Agroove 190 may be formed in the edge region 180.

FIG. 5B shows the groove 190 extending from the first main surface 101into the parent substrate 100. The groove 190 may be formed in ahorizontal main section of the first main surface 101 and may have anyof the cross-sectional shapes as described with reference to FIGS.4A-4E, by way of example. In addition, a grid-shaped dicing grid (notillustrated) may be formed in the kerf region 116, wherein a verticalextension of the dicing grid may be smaller than a vertical extension ofthe groove 190.

An auxiliary carrier 300 may be attached to the front side of the parentsubstrate 100. For example, an adhesive layer 200 may adhesion-bond theauxiliary carrier 300 onto the first main surface 101 with the frontside metallization 171. The adhesion layer 200 may be formed from atemporary bonding/debonding adhesive. For example, liquid glue may beapplied onto the front side of the parent substrate 100. The glue mayfill at least partly the groove 190 and voids between neighboringportions of the front side metallization 171. A pre-bake may dry theglue and/or may remove a portion of a solvent contained in the glue. Theauxiliary carrier 300 may be brought into contact with an exposed topsurface of the dried glue. The dried glue may be cured, for examplethrough illumination with ultraviolet radiation, to form the adhesivelayer 200.

A laser beam 800 may be directed to the exposed second main surface 102of the parent substrate 100 to form a detachment layer 150 in thecentral region 110 as shown in FIG. 5A.

FIG. 5C shows a wafer composite 890 including the parent substrate 100with the front side adhesion-bonded to a working surface 301 of anauxiliary carrier 300. The auxiliary carrier 300 may be a glass plate, asapphire plate or may include a plate from the material of the mainportion of the parent substrate 100. For example, the auxiliary carrier300 may include polycrystalline or crystalline silicon carbide. Theadhesive layer 200 may fill spaces between neighboring portions of thefront side metallization 171. The adhesive layer 200 may fill the groove190 and may form a meniscus spanning from the chamfer 185 of the parentsubstrate 100 to the working surface 301 of the auxiliary carrier 300.

The laser beam 800 penetrates through the second main surface 102 at theback side of the parent substrate 100 and forms modified structures 151in a detachment layer 150. The modified structures 151 may includeanother phase of the semiconductor material of the parent substrate 100,for example elemental silicon and elemental carbon, for exampleamorphous carbon. The modified structures 151 may form modified stripesextending orthogonal to the cross-sectional plane. In addition, thedetachment layer 150 may include microcracks 154 generated by mechanicalstress induced by the thermal heating through the laser beam 800 and/orvolume expansion through the phase change of the semiconductor material.The detachment layer 150 cuts the inner groove sidewall 191. In otherwords, the microcracks 154 of the detachment layer 150 may end at theinner groove sidewall 191.

According to the example illustrated in FIGS. 5A-5C, the groove 190 isformed at the front side of the parent substrate 100 prior to attachingthe parent substrate 100 with the front side down to the auxiliarycarrier 300. According to another example (not illustrated), the groove190 is formed at the back side of the parent substrate 100, e.g. afterattaching the parent substrate 100 with the front side down to theauxiliary carrier 300.

Prior to or after forming the detachment layer 150 an auxiliaryradiation beam 810 may be directed onto a peripheral adhesive portion280 of the adhesive structure 200 as illustrated in FIG. 5D. Forexample, the auxiliary radiation beam 810 may be directed exclusivelyonto the peripheral adhesive portion 280 through the auxiliary carrier300.

FIG. 5E shows a wafer composite 890 including the parent substrate 100and the auxiliary carrier 300 after removal of the peripheral adhesiveportion 280. A central adhesive portion forms an adhesive structure 210that connects the parent substrate 100 and the auxiliary carrier 300.The groove 190 is free from solid material and may be filled with afluid, for example with ambient air or a process gas.

A splitting process induced by volumetric lattice stress is carried out.The volumetric lattice stress may be induced by application ofultrasonic waves or by a polymer foil attached to the second mainsurface 102 at the back side of the parent substrate 100 and cooled downto below the glass transition temperature of the polymer foil.

As illustrated in FIG. 5F the detachment layer 150 of FIG. 5E splitsalong a ribbed splitting surface 155 that ends at the inner groovesidewall 191. A first parent substrate portion between the first mainsurface 101 and the splitting surface 155 may form a device substrate410 with a thickness of less than 200 μm, for example less than 100 μmor less than 50 μm. From the device substrate 410, a thin devicesubstrate may be obtained as described below. A second parent substrateportion between the second main surface 102 and the splitting surface155 forms a reclaim substrate 420. From the reclaim substrate 420 afurther device substrate may be obtained by suitable processes.

The ribbed splitting surface 155 may be planarized, for example grindedand/or polished, e.g., in a chemical/mechanical polishing process and/orby a heat treatment in an atmosphere containing hydrogen. Theplanarizing process may include exposing a dicing grid provided that adicing grid is formed according to a DBG approach. Backside processingfor finalizing a vertical power conductor device may be performed. Thebackside processing may include implanting dopants of at least oneconductivity type and forming a back side metallization.

FIG. 5G shows a processed device substrate 450 obtained from the devicesubstrate 410 of FIG. 5F. The processed device substrate 450 includes aheavily doped contact region 129 formed along a back side surface 452and a voltage sustaining layer 121 formed between the contact region 129and the emitter regions 120. The voltage sustaining layer 121 mayinclude a low-doped drift zone and/or a superjunction structure withcomparatively heavily doped p-type columns and n-type columns extendingin a vertical direction. A back side metallization 172 may be formed onthe back side surface 452.

FIGS. 6A-6C refer to a layer transfer process combined with an epitaxyprocess, wherein the transfer layer may be obtained from a semiconductorwafer by a splitting process as described above.

A groove 190 is formed in the edge region 180 of a parent substrate 100,for example by an edge trim. The first main surface 101 at the frontside of the parent substrate 100 is attached to an auxiliary carrier300. For example, the first main surface 101 and the working surface 301of the auxiliary carrier 300 may be direct-bonded to each other.According to the illustrated embodiment, a thermally stable bondinglayer 250 may be provided between the first main surface 101 of theparent substrate 100 and the working surface 301 of the auxiliarycarrier 300. A detachment layer 150 is formed in the parent substrate100 as described above.

FIG. 6A shows the detachment layer 150 ending at an inner groovesidewall 191. The bonding layer 250 mechanically connecting theauxiliary carrier 300 and the parent substrate 100 may be or may includea silicon nitride layer, a structured layer containing silicon nitride,a layer including heavily doped crystalline silicon carbide and/orpolycrystalline silicon carbide, by way of example. The auxiliarycarrier 300 may consist of or may include the material of the parentsubstrate 100. In case the parent substrate 100 is a silicon carbidecrystal, the auxiliary carrier 300 may also be a silicon carbidecrystal, for example a silicon carbide crystal with inferior crystalquality.

A splitting process as described above separates a second parentsubstrate portion (reclaim substrate 420) from a first parent substrateportion (device substrate 410) along a ribbed splitting surface 155horizontally extending through the detachment layer 150 of FIG. 6A.

As shown in FIG. 6B the ribbed splitting surface 155 of the devicesubstrate 410 may be polished and/or planarized to some degree, whereinthe height of the ribs may be reduced. The device substrate 410represents a transfer layer suitable as starting layer for an epitaxyprocess. An epitaxial layer may be formed on the device substrate 410.Front side processing may form structures of integrated circuits inand/or on the epitaxial layer.

FIG. 6C shows a processed device substrate 450 including the devicesubstrate 410 and an epitaxial layer 430 obtained by epitaxial growth onthe device substrate 410. Emitter regions 120, an interlayer dielectric160 and a front side metallization 171 may be formed in and/or on theepitaxial layer 430 as described above.

The processed device substrate 450 may be separated from the auxiliarycarrier 300. For example, the bonding layer 250 may be selectivelyremoved or a further laser-induced splitting process may be effective onan upper portion of the auxiliary carrier 300.

FIGS. 7A-7B refer to a method of forming the groove 190 after mountingthe parent substrate 100 onto an auxiliary carrier 300.

As shown in FIG. 7A the parent substrate 100 may be a parent substrateas described with reference to FIG. 5A. The parent substrate 100 may beconnected with the front side down with the auxiliary carrier 300through an adhesive layer 200. A tilted laser beam 800 may be directedfrom the back side onto the second main surface 102.

The laser beam 800 may impinge vertically on the second main surface102, wherein vertical grooves may be formed that extend from the secondmain surface 102 into the parent substrate 100. The grooves 190 may haveany of the shapes as described with respect to FIGS. 2 and 4A-4F forgrooves that extend from the first main surface 101 into a parentsubstrate 100.

According to the illustrated embodiment, a propagation axis 801 of thelaser beam 800 is tilted to a vertical direction 104 by a tilt angle θ.The tilt angle θ may be in a range from 10 degree to 80 degree, by wayof example. The laser beam 800 may induce a plasma etch, which may becontrolled to form a tapering groove 190 that ends in a plane of thedetachment layer 150. Alternatively, the groove 190 may cut the plane ofthe detachment layer 150 and/or may be slightly laterally displaced fromthe detachment layer 150 by some microns. For example, the verticalextension of the groove 190 with respect to the second main surface 102may be equal to or greater than a second distance d2 between the secondmain surface 102 and the detachment layer 150.

The shape of the inner groove sidewall 191 and the shape of the outergroove sidewall 192 may be controlled by parameters of the plasma etch,for example energy, angle and impinging area. For example, the innergroove sidewall 191 may be inwardly bowed with respect to the groove 190and outwardly bowed with respect to the portion of the parent substrate100 between the second main surface 102 and the detachment layer 150.Accordingly, the outer groove sidewall 192 may be formed to extendinwardly with respect to the groove 190 and outwardly with respect tothe substrate portion between the first main surface 101 and thedetachment layer 150.

According to the example illustrated in FIGS. 7A-7B, the groove 190 isformed at the back side of the parent substrate 100 after attaching theparent substrate 100 with the front side down to the auxiliary carrier300. According to another example (not illustrated) the groove 190 isformed at the front side of the parent substrate 100 prior to attachingthe parent substrate 100 with the front side down to the auxiliarycarrier 300.

FIG. 8A shows a portion of a wafer composite 890 including a parentsubstrate 100 with a chamfer 185, a groove 190 and a detachment layer150 cutting a vertical sidewall section 193 of the inner groove sidewall191. The chamfer 185 is a part of an outer lateral surface 103. Anadhesive layer 200 formed between the first main surface 101 of theparent substrate 100 and a working surface 301 of an auxiliary carrier300 mechanically connects the parent substrate 100 and the auxiliarycarrier 300.

Forming the groove 190 before mounting the parent substrate 100 onto theauxiliary carrier 300 avoids the ablation of debris and may be performedwith existing tools, for example a conventional edge trimmer. The edgetrimming process may be comparatively fast and cheap. Existing tools foredge trimming allow for a fast integration of the process in a processline. The auxiliary carrier 300 remains unharmed and may be reusedwithout extensive rework.

FIG. 8B shows a grinding pad 850 of a bevel wheel etch trimmer. Theshape of an indentation 851 of the grinding pad 850 may shape the outerlateral surface 103 of the parent substrate 100, wherein a groove 190 isformed at the front side of the parent substrate 100. In addition, thegrinding pad 850 may shape bevels along the outer lateral surface of thedevice substrate 410 and the reclaim substrate 420. Multipleindentations 851 may reduce process time.

In FIG. 9A the groove 190 extends from the first main surface 101 intothe parent substrate 100. The groove 190 is formed at a distance to thelateral outer surface 103. Forming the groove 190 may include a cut witha round-cut blade. Forming the groove 190 may, in addition or as analternative, include linear dicing and/or grinding in a portion parallelto a flat portion of the lateral outer surface 103. Alternatively, thegroove 190 may be formed by at least one of: (i) a laser ablationprocess or a laser-assisted etch process, for example by using UV(ultraviolet) laser radiation, (ii) a plasma and/or patterned etchprocess, e.g., RIE (reactive ion beam etching) and/or (iii) electricaldischarge machining (EDM) and/or electro-chemical discharge machining(ECDM).

According to FIG. 9B a spiral cut or a plurality of round-cuts withdifferent diameters may form a groove 190 that extends outwardly up tothe lateral outer surface 103.

FIG. 10 shows a groove 190 formed by front side micro machining. Theprocess may use UV ablation using a tilted laser beam. The ablationvolume may be comparatively small and both a chamfered device substrate410 and a reclaim substrate 420 with chamfered stiffing ring 427 may beformed.

FIGS. 11A-11D refer to embodiments using back side micro machining. Theprocess may use UV ablation using a tilted laser beam. The process maybe performed after mounting the parent substrate 100 onto an auxiliarycarrier 300. The tilted laser beam 800 may be controlled to form both achamfered reclaim substrate 420 and a device substrate 410 withchamfered stiffing ring 417. The impinging site for the ablation laserbeam 800 may be selected to achieve both a favorably chamfered reclaimsubstrate 420 and a favorably shaped stiffing ring 417. Alternatively orin addition, the impinging site for the ablation laser beam 800 may beselected to avoid ablation of a portion of the adhesive layer completelyor to a high degree.

Forming the grooves 190 may include a laser-assisted material removal,wherein the laser-assisted material removal may include directing alaser beam completely or partly onto a lateral outer surface 103 of theparent substrate 100 and wherein a tilt angle between a propagationdirection of the laser beam and a horizontal plane is at least 20degree, e.g., at least 30 degree.

In FIG. 11A the groove 190 extends from an outermost edge of the secondmain surface 102 into direction of the lateral end of the detachmentlayer 150.

In FIG. 11B a tilt angle β between the vertical direction 104 and alaser beam axis 801 of the laser beam 800 is about 30 degree. Theimpinging site is completely within the strictly horizontal main portionof the second main surface 102.

In FIG. 11C the tilt angle β is about of 30 degree and the impingingsite is predominantly within a slightly chamfered portion of the secondmain surface 102 and to some degree on the lateral outer surface 103.

In FIG. 11D the tilt angle 1 is about 75 degree. The impinging site iscompletely on the lateral outer surface 103.

In each of the examples illustrated in FIGS. 11A-11D, the groove 190 isformed at the back side of the parent substrate 100 after attaching theparent substrate 100 with the front side down to the auxiliary carrier300. According to other examples (not illustrated) the grooves 190 areformed in the same way as illustrated but at the front side of theparent substrate 100 prior to attaching the parent substrate 100 withthe front side down to the auxiliary carrier 300.

FIG. 12 schematically shows a machining apparatus 900 for tilted laserablation along the circumference of crystalline parent substrates witharbitrary horizontal cross-section. A profile sensor unit 910 may obtainshape information about the shape of the parent substrate 100. A scanunit 920 may generate a laser beam 800 impinging on the parent substrateat an angle between 10 degree and 80 degree with respect to a verticaldirection and may control the position of an impinging site of the laserbeam 800 on the parent substrate. A wafer composite 890 including theparent substrate may be temporarily mounted on a stage unit 940. Thestage unit 940 may allow rotational and/or linear movement of the wafercomposite 890 relative to the profile sensor unit 910 and the scan unit930.

A control unit 920 may process information obtained from the profilesensor unit 910 and, if applicable from the stage unit 940, and maycontrol a relative movement between the scan unit 920 and the stage unit940 in a way that the laser beam 800 follows a desired path on thesurface of the wafer composite 890.

The machining apparatus 900 allows formation of any of the grooves asdescribed above, in particular of grooves 190 as described withreference to FIGS. 4A-4E, 10, and 11A-11D.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A machining apparatus, comprising: a profilesensor unit configured to obtain shape information about a parentsubstrate; and a laser scan unit configured to direct a laser beam ontothe parent substrate, wherein a laser beam axis of the laser beam istilted to an exposed main surface of the parent substrate, and wherein atrack of the laser beam on the parent substrate is controllable as afunction of the shape information obtained from the profile sensor unit.2. The machining apparatus of claim 1, wherein the machining apparatuscomprises a stage unit.
 3. The machining apparatus of claim 2, whereinthe stage unit is configured to allow rotational and/or linear movementof a wafer composite comprising the parent substrate relative to theprofile sensor unit and the laser scan unit.
 4. The machining apparatusof claim 2, wherein the stage unit is adapted to be reversibly connectedwith a main surface of the parent substrate.
 5. The machining apparatusof claim 2, wherein the stage unit is moveable with respect to the laserbeam and/or the laser beam is moveable with respect to the stage unitsuch that the laser beam may follow a track along the circumference ofthe parent substrate.
 6. The machining apparatus of claim 2, wherein themachining apparatus comprises a control unit that is configured toprocess information obtained from the profile sensor unit and from thestage unit.
 7. The machining apparatus of claim 6, wherein the controlunit is configured control a relative movement between the laser scanunit and the stage unit in a way that the laser beam follows a desiredpath on a surface of a wafer composite comprising the parent substrate.8. The machining apparatus of claim 1, wherein the machining apparatusis configured to form a groove in an edge region of a wafer compositecomprising the parent substrate.